1. Field of the Invention
The present invention relates to a liquid crystal display device, and particularly to a spacer arrangement of a liquid crystal display device of a latitudinal electric field type.
2. Description of the Prior Art
Recently, liquid crystal display (LCD) devices have been widely used for display terminals of various information instruments, making use of beneficial characteristics of the LCD devices such as light weight, thinness and a reduced power consumption. Typically, most of these LCD""s are of TN (twisted nematic) and STN (super twisted nematic) types. Such conventional longitudinal electric field type LCD""s have been put to practical use, but have a problem of a relatively narrow viewing angle. As such, there has been proposed an LCD of a latitudinal electric field type, i.e., an In-Plane-Switching (IPS) type.
Such an LCD of IPS type is disclosed in U.S. Pat. No. 5,995,186 issued on Nov. 30, 1999. In this LCD, pixel electrodes and common electrodes are formed on a thin film transistor (TFT) substrate. Both electrodes are formed in comb-teeth shapes, and arranged to oppose to each other via insulation layer. No electrodes are formed on a color filter (CF). Spacers of small particles are arranged and a liquid crystal is sealed, between the TFT substrate and the CF substrate.
Since such an IPS type of LCD has a wider viewing angle, there is an increased demand as a substitution for a conventional CRT display. However, one of the problems in adopting small particles as spacers is that it is not determined as to what positions (in-plane positions) the particles are arranged at, upon adopting general dispersing means. If a spacer such as a plastic bead is positioned on a pixel, the display quality of the liquid crystal display element is degraded due to scattering and transmission of light by the spacer. There is another defect that the spacer has a spherical shape which contacts at points upon cell pressing, which leads to damage of an alignment film and a transparent electrode, tending to occurrence of a display defect. There is a further defect that the liquid crystal is contaminated and its resistant voltage is lowered due to damage of the alignment film and transparent electrode. Moreover, since it is required to provide a process for uniformly dispersing the spacers and to control a particle size distribution of the spacers at a high precision, it has been difficult to obtain a stable display quality with a simplified manufacturing method.
In Japanese Patent Application Laid-Open No. HEI-10-48,636 (48,636/1998) laid open on Feb. 20, 1998, there is disclosed an IPS type of LCD for solving such a problem. In this improved LCD, a columnar spacer laminated with color filters is provided on a CF substrate, instead of adopting a small particle as a spacer. The spacer formed in such a structure eliminates a necessity of additional process in a conventional manufacturing process for a color filter, thereby providing an advantage that the color filter can be fabricated at a cost equal to the conventional one.
Further, in this improved LCD, the spacer position is limited to an intersection between a data line (drain electrode wire) and a scan line (gate electrode wire) in view of avoiding a rubbing inferiority. However, there has been found such a problem that a long-term afterimage phenomenon tends to occur when the spacer is arranged over the data line or the scan line having a high potential. This phenomenon means a situation where a certain pattern displayed in a bright state for a long time fails to return to its fully dark initial state and rather exhibits a pattern seizure or sticking, even when it is tried to return the pattern as noted.
It is therefore an object of the present invention to provide an active matrix type LCD (AM-LCD) of an IPS type capable of reducing the occurrence of such a long-term afterimage phenomenon.
The liquid crystal display device of a latitudinal electric field type of the present invention is characterized in that a forming position of a protruded spacer is limited to over a common electrode wire or an extended portion of a pixel electrode, to thereby reduce the occurrence of the aforementioned long-term afterimage phenomenon.
According to one embodiment of the present invention, a first substrate as a TFT substrate is provided with, for each of a plurality of pixels arranged in a matrix, a gate wire arranged at one side of a periphery of the pixel, a drain wire arranged perpendicularly to the gate wire at another side of the periphery of the pixel, a common electrode wire arranged at the other side of the periphery of the pixel in parallel with the gate wire, a common electrode extended from the common electrode wire perpendicularly to this common electrode wire, and a pixel electrode arranged in parallel with the common electrode in a mutually spaced manner. A second substrate provided with a color filter is arranged so as to oppose the first substrate and a liquid crystal layer is sealed into a gap formed between the first substrate and the second substrate by means of a spacer. The spacer comprises a protruded portion provided on at least one of the first substrate and the second substrate, and that a contact portion, at which the first substrate and the second substrate contact each other via the protruded portion, is located on at least one of the common electrode wire and an extended portion of the pixel electrode.
The liquid crystal display device is also characterized in that the common electrode is plural, the extended portions of the pixel electrode are formed to overlap with the common electrode wire, and the contact portion is located over the extended portions of the pixel electrodes.
Further, the liquid crystal display device is characterized in that the pixel electrode is plural, portions of respective adjacent pixel electrodes are formed to overlap with the common electrode wire, and the contact portion is located between the adjacent pixel electrodes and over the common electrode wire.
Moreover, the liquid crystal display device is characterized in that a portion of the pixel electrode is formed to overlap with a gate wire of an adjacent pixel in the extended direction, and the position of the contact portion is located over the overlapped position.